General Organic Chemistry- Quick notes with JEE Advanced concept

Inductive Effect:-

Def:-It refer to phenomenon where in a molecule a permanent dipole arises due to unequal sharing of the bonding e- in the molecule. This effect travel via sigma bond only.

Types:- +I and -I

+I shows to donate e-

-I shows to withdraw e- density

Important points:-

• I.E depends upon distance

• Atoms having -ive charge shows +I effect and vice versa

Ex- Fe+3>Fe+2>Fe+ (-I effect)

• If s% increases E.N increases and -I increases

• No. of C increases in same hybridisation -I increases

• I.E also depends on summation of charge 

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Resonance:-

Delocalisation (Shifting) of bonding orbitals is called resonance

Condition for resonance:-

• Conjugation should be present

• Compound should be planar

Trick:-

• = - +

• = - -(negative charge)

• = - :(lone pair)

• = - triple bond

• = - =

Resonance hybrid actually exists but resonance structure are hypothetical

Bond order:- Total no. of bonds/total reso. Struc.

                      Bond order ∝ 1/Bond length

Stability:- Stability ∝ Resonance

Importants points:-

• Initial net charge should be equal to final charge

• The reso. Struc. having no charge seperation are more stable

• The position of the atom remains fixed in all the resonance structure

• Adjacent +,- are unstable in resonating structure

• Stability of charged species < stability of neutral species

• The structure having more benzoid rings it will be more stable 

• - is more stable on E.N element and + is also more stable on E.N only if octet is completed

• If a element have + charge is more stable than element having + charge which is more E.N than that element i.e O+<N+

• Structure having more pie bonds is more stable

• Octet completed species are more stable

• 

Resonance-Mesomeric Effect:-

  Whenever a molecule is in resonance, charge depletion take place at one end is known as mesomeric effect

+M-- Donates e- density

-M-- Withdraw e density

Important points:-

• If any central atom of group have L.P or negative charge it will show +M 

• If any central atom of group have vacant orbital e.g S have 3d empty orbital

Heat of hydrogenation:-

Amount of energy released whenever we add H2 to a species

ΔH- energy released-Exothermic 

Exothermic reaction have always negative energy.

Heat of hydrogenation ∝ 1/Stability ∝ 1/Resonance Energy

Heat of Combustion:-

Whenever a compound is burned presence of O2, energy is released called Heat of combustion

Heat of Combustion ∝ 1/Stability ∝ 1/Resonance Energy

Hyperconjugation:-

• Hyperconjugation is a kind of resonance and also called no bond resonance

• No. of hyperconjugation struc. = no. of α carbon’s Hydrogen

• No. of hyperconjugation struc. ∝ Stability

• H.C also called Baber Nathan effect

• 

Hyperconjugation in π Bonds:-

 

Hyperconjugation in Carbocation:-

• These are e- deficient species

• It have sp2 hybridisation

• Vacant orbital present

• Carbocation can also show H.C due to vacant orbital 

• No. of H.C struc. = no. of α carbon

• To stabilize it will need e- donating group 

• More +I then more stability also increases

• If E.N increases for carbocation then stability decreses

•  

Hyperconjugation in Radicals:-

Have same property as Carbocation.

Important points about benzene rings:-

 

• + travelsat the ortho/para position only

• Resonance effect only travel at ortho/para position

• 

Bridge Head Carbocation

• A-B common between two rings

• Non planar species

• Bridge C+ least stable

• No resonance and no Hyperconjugation

• 

 Sigma bond Resonance:-

• Also known as Dancing resonance

• Very high angle strain 

• Very unstable breaks easily to release angle strain

• If + , - is present on a benzene ring then resonance is not possible because they go out of plane 

• More no. of ⊳- on C+ more stable compound

• + charge is available on bridge head so it is unstable

Stability of Carboanion:-

• e- rich species

• Stabilise with e- withdrawing species i.e. -I

• No hyperconjugation is shown 

• Reverse hyperconjugation is shown

• 

Aromaticity of compound:-

Huckles rule to be aromatic-

 

• Cyclic compound 

• Planar compound

• (4n+2)𝝿 conjugated e- must be present (conjugated means boundary e-)

• Aromatic compounds are highly stable

Anti aromatic compound:-

• Cyclic compound

• Planar compound

• 4n𝝿  conjugated e- must be present 

• Anti aromatic compound are highly unstable

Non aromatic compound:-

• Cyclic

• Non planar compound

Stability order:-

                       

               Aromatic > Non aromatic > Anti aromatic

               Acids and Bases

Acids:-

HA ⇋ H+   +   A-

              (conjugate base)

• If a compound is good acid forward rxn > backward rxn

• If A- is stable then the rxn goes in forward direction 

• If A- is unstable then the rxn goes in backward direction

• If stability of A-(conjugate base) ↑ then acidity ↑

• Conjugate base is formed only when H+ will be formed or removed

• 

Stearic Inhibition of resonance:-

In order to minimise the repulsion -I goes out of the plane is called S.I.R

• As it become non planar so no resonance

• In case of halogen on the aromatic ring the inductive effect dominates over mesomeric effect

• In case of halogen on the aromatic ring the inductive effect dominates over mesomeric effect

• 

Feasibility of reaction:-

HA + Base ⇋ Salt + HA’

Acid(HA):-   HA  ⇋  H+  +  A-

Acid(HA’):-  H+  +  A’- ⇋  HA’

If stability of:-

                    A- >A’- (Feasible)

                    A- <A’-  (Unfeasible)

∴ HA > HA’ (Strength of acid )

• If S.A goes to W.A then the rxn. Is feasible 

• Poly hydroxy alcohol > H2O > Mono hydroxy alcohol (Acidity)

Ortho Effect :-

• Applicable on -COOH , -NH3 

• Special case of S.I.R

• Ortho effect increase the acidity of the benzoic acid

• Bulkiness ↑ acidity ↑

• In ortho effect due to same on benzene ring at ortho position, make the ring non planar and stability ↓

• Ortho effect is highest for Meta > Ortho > Para

• For position -I ↑ acidity ↑ 

•                                                           comparison of stability   

• 

Base :-

B: + H+  ⇋  BH

         (conjugate acid)

• If a conjugate acid is highly stable then it is good base

• Something that donates L.P fastly it is good base

• For finding good base react base with H+ then conjugated will form if that conjugate acid is highly stable then that is good base e.g. CH3-NH2 , NH3……….it will become CH3-NH3+ , NH4+

• These all above Carbocation are stabilise by +I so ….+I ↑ Stability ↑ Basicity ↑

• %S (s orbital ) ↑ lone pair donation ↓ so Basicity ↓

Basic Strength in aqueous solution:- 

NH3 + H+ ⇾ NH4+

CH3-NH2  + H+ ⇾ CH3-NH3+

• Basicity of compound in gaseous state is not same is aq. Soln. 

• In aq. Soln. medium the basicity is a net effect of e- density and soluation energy.

Some most important relation, very useful for question solving:-

Boiling point

B.P ∝ Surface area of molecule ∝ extent of inter molecular H-Bonding ∝ dipole moment

Acidic Strength

Acidic strength ∝ Ka ∝ 1/PKa ∝ -I , -M , -H attached ∝  1/ +I , +M , +H ∝ Stability of conjugate base 

Stability of Alkenes ∝ No. of Hyperconjugation

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